In German Patent Document De 32 27 187 C2, a scrubber for the purposes described is disclosed in which the sump collecting the scrubbing liquid from the absorption zone has a conical configuration to avoid calcium sulfate deposits during the operation of the scrubber. A circulation unit is connected to the sump having an intake at an upper location of the sump, a pump and outlet means formed in a lower part of the sump. Before the scrubber is brought into operation after a standstill the circulation unit is turned on for a short time to dissolve deposits which have collected in the apex of the cone during the standstill mode of the scrubber. When the scrubber is in operation and thus in a stationary state, the circulation unit is shut down and thus is not effective.
In practice it is found that the conical part of the sump, which provides the reaction zone, must have a significant height in order to achieve internal mixing and forming of calcium sulfate. With a substantial height of the sump, however, the overall height of the column or tower may be so great that structural problems can result. For example, the tower may have to be reinforced to withstand the higher wind forces to which the tower may be subject because of the greater height necessitated by the sump.